The present invention relates to a rolling element screw device for converting a rotary motion into a linear motion, in which a nut member is threadingly engaged with a screw shaft through the intermediation of rolling elements.
As the above-mentioned rolling element screw device, for example, there is known a rolling element screw device of a type in which an endless circulation path for rolling elements is formed using a circulation component. The rolling element screw device of this type includes: balls as a large number of rolling elements; a screw shaft having an outer peripheral surface in which a spiral ball raceway groove is formed; a nut member which includes a spiral loaded rolling element raceway groove opposed to the ball raceway groove, and is threadingly engaged with the screw shaft through the intermediation of the balls; and a circulation component mounted to the nut member to form an endless circulation path for the balls (JP 11-51049 A).
The circulation component is formed into substantially a U-shape, and includes a pair of first circulating portions fitted onto a peripheral wall of the nut member, and a second circulating portion coupling the pair of first circulating portions together. The circulation component enables the balls to roll inside the circulation component from one of the first circulating portions to another one of the first circulating portions. Each of the first circulating portions is formed into a cylinder having substantially an elliptical cross-section, and in each of the first circulating portions, a ball introducing hole extending in a tangent direction along a lead angle of the loaded rolling element raceway groove is formed. On the other hand, a pair of pipe mounting holes, into which the first circulating portions of the circulation component are inserted, respectively, is formed in the nut member. The pair of pipe mounting holes is formed astride several turns of the loaded rolling element raceway groove of the nut member.
When the first circulating portions of the circulation component are fitted into the pipe mounting holes of the nut member, the following configuration is obtained. Specifically, each of the first circulating portions slightly protrudes from an inner peripheral surface of the nut member. The balls, which finish rolling on a loaded rolling element raceway track formed of the ball raceway groove of the screw shaft and the loaded rolling element raceway groove of the nut member, are scooped up into the circulation component to be brought out of the loaded rolling element raceway groove of the nut member, and then are returned to a start position of the loaded rolling element raceway track. That is, the circulation component is mounted to the nut member, and thus the endless circulation path for the balls is completed.    [PTL 1] JP 11-51049 A